IMPLICATIONS OF WATER SOLUBILITY EXPERIMENTS FOR THE TAPHONOMY OF EGGSHELL CUTICLE

Certain lineages of dinosaurs, including modern birds, produce hard-shelled eggs with the exteriors coated in cuticle. This protective covering permits the diffusion of essential gases through the shell whilst simultaneously providing the interior of the egg protection from the infiltration of water and bacterial attack. Cuticle is poorly represented in the fossil record of non-avian dinosaurs. This was illustrated when running energy dispersive X-ray spectroscopy (EDS) to determine elemental abundances in eggshell fragments collected from the Early Cretaceous Mussentuchit Member of the Cedar Mountain Formation. It is postulated that the absence of preservation is due to the rapid degradation of cuticle during taphonomic processes. To test this hypothesis, the solubility of an emu egg was determined by submerging shell fragments of equivalent size in deionized water for set durations. Solubility was investigated because surface and ground water exposure is a postulated driver of cuticle degradation during transport. Emu eggs were chosen due to their shell thickness and rugose ornamentation, which, among modern birds, makes them morphologically most similar to the Mussentuchit Member theropod eggs analyzed in this study. Following various submersion times, the emu eggs were analyzed using EDS. The resulting data showed that the primary elements comprising cuticle: P, Cl, Mg, and K (outside of Ca, C, and O) were significantly from the original, unaltered state after 30 minutes of submersion. These experimental results show that cuticle is highly soluble, explaining its rarity in the fossil record. Unless rapidly buried prior to transport and dissolution, the cuticle has a low probability of surviving long enough to undergo fossilization.